Phase inverter circuit



Nov. 26, 1946. s. BERKOF'F 2,411,706

PHASE INVERTER CIRCUIT I Filed June 3, 1942 2 sheets-sheet 2 UUTPl/T l 0UTPUT 2 Ivemtor: Segmour Ber-kof?,

` His AttoT-neg.

Patented Nov. 26, 1946 Y STATE-s roFFici;

2,411,706... .I HXsiNvimrERcntciiii? Seymour' Berkoff, Bridgeportfonni; assignorf to General Electric= Company;-y a,corporationfo New' York- 1o Claims. (01.4 iis-171!) l e naif-comprising a' 'seriesr of veryf short pulses i at somewhai-irregular intervals', the 'phaseiiniierter use@ toconvert this single'signalvinto'two' sig-v nais `lfor feeding, foit example; ltWo -push pull ari-` plii'ers should f provide l'outplltsignals which are'y equal;andfoppositeinphase: Itis desirable both that there beno/ti-medelay' between the input pulse and eitherlof the output pulses and that there be no amplitude'distrtoi ifthe phase inverter circuit. iiziyjiiivein'i'ioiiH proposes io eliminate both iimedeigiya'ric iciiiiiitiiae'disiortion in such a pulse ainplifie'rbyeiiiployirig'la balanced impedance bridg't'o'f redue'tleffect of feedf back onv the control gridi A to vary the; relative magnitude' of tliltwo output4 single-:ended: source* is connected acossfpints" r'erotef` from the tvvo output points." 'Another' feature is the proportioning of` the'values' ofKL the impedances comprisingr thisf bridge f' so that the magnitudes of= the output signals will be exactly" proportionaltothe-magnitudeothe input signal.

A Theifeatures'ofmy inventiomwhich Iv` believe to, be novelr a-re set forth with particularityl in theappendedei-aimsf My invention itself how-w ever, togetherr Withr furtherfobjectshand advanlf` tages thereof;A may best be understood` byA refer- L ence tothe' following-description takenin connection'fwith--theaccompanyingdrawing's; l in 'f which' Fig;Ayv 1-r is 'adiagram-'off a phase=inverter circuit embodyingmyinvention; Figi 2'; is-y af' scl'i'ematic'y diagrammi/the'phaseinvertercircuitof Fig; 1f f inwhiclfrl the* impedance bridge is illustrated ;v Figs. Scand if areephase inverter circuits showing m'odicatioils IAOffthe invention; andi 'Figi'- 5 iss a? sf'zhem'aticF diagramof; the' circuit' of' Fig;' 4'A iiir vvl-iiclrtlieimpefdancelorldge'isiillustritedir In f'the circuitfy of Figi 1'? a'irelectron` discharge' device*- I I e, '.Whichii'nayfbe an1 audio-frequency a'mzpli'e'rfof: ai irdio" receiver; furnishes a signal ito' f'a second? electron discharge" device*y l 2l acting: asi a singlerltubec phase@ inverter." The electron dise Since? trie' anode resistance' 2'4- not' a lieaf rs'staifice; butvarie's; fo'ifa fixedH grid pot'etiz'il;A witiif'aiiodeff potentiel,A introduction of distortioniitftlfgid circuit of' device I'Zf'is prevented' byiise* oi"-iesisifciT 22 to establish' theVT bridge re: lationship illustrated in Fig. 2. If resistorsZD andi 21 are ei'u-l-, i"e'zsi`stol1s"22V andl 231ar`l eqial, tiiefeiiect'i's triatcifa completely balanceo Bridge scf trici discoiiioircaiinoif arise' erection dis:

ape the oiiipiitfcirciiitsof inefoiiseiriveiieii me@ 2f fe?, tiieifewiiivceffoieeciriefseek off'po'@ teniieiserisigf'iii the output circuit' of ytime lizinstitue -oriiiibefl l; 'mieifoiaihe volt;-

2l are automatically equal and opposite and of the same time occurrence as the input signal supplied tothe control electrode I6.

By the above-outlined circuit my invention provides a single tube phase inverter circuit which may be used in pulse circuits. When a signal is supplied to the preceding amplier Il and after amplification is supplied to the control electrode of tube I2, by means of the balancedbridge circuit, two pulses, one positive-going and the other negative-going, and of exactly the same time occurrence, are provided at the two output points. In this circuit, because of the balanced bridge relation, the phase inverter will have equal impedance with respect to both output I and output 2. Such a relationship between output impedances is desired, for example, where each of the two output signals is transmitted through an appreciable length of cable having a definite impedance characteristic before arriving at its destination and is attenuated during such transmission. If the eiect of such a capacitive load across resistor 2I alone is considered, it will be seen that, because of attenuation, less degeneration occurs in the cathode circuit for higher frequencies. As a result the tube gain becomes larger lfor higher frequencies than for lower, that is, a greater higher frequency voltage appears across resistor 20 than appears across resistor 2l. On the other hand, if the same capacitive load is shunted across resistor 20 alone, the higher frequency voltages across resistor 20 are less than those across resistor 2 I. Hence if equal capacitive loads are shunted across these two resistors, the upper frequencies across resistor 20 will be reduced in magnitude to practically the same value as those existing across resistor 2 I. The net effect of equal capacities across the anode and cathode circuits is therefore to keep the frequency response in the two circuits approximately the same, and the pulse shapes remain equal. Thus, with the equal output impedances of the phase inverter circuit provided by my balanced bridge arrangement, equal wave forms of the signal voltages at their destinations will be obtained.

In the phase inverter circuit of Fig- 1 resistor 22 is shown connected directly between the anode and control electrode of electron discharge device I2, a negative bias for the control electrode being maintained by the resistor I9. In certain applications it may be desired to block the control electrode from the anode potential. In Fig. 3 is shown a modification of my invention wherein the capacitor 2B is connected in the circuit between the control electrode and anode in series with the resistor 22. In order that the operation of my balanced bridge remain appreciably unaffected by the added impedances of capacitor 26, this capacitor should have a negligible impedance, at the lowest frequency to be amplified, as compared with the impedance ofresistor 22. Since the value of resistor 22 is quite large and since the frequency of signals being amplified is usually very high, the requirement of negligible impedance for capacitor 26 is easily met.

In Fig. 4 is shown a modification of my phase inverter circuit which is applicable where it is desired to vary the relative magnitudes of the two output voltages. Such flexibility may be desired, for example, to compensate for inequalities in two push pull amplifiers following the phase inverter. In this arrangement the variable resistor 2'I is connected in the anode circuit between the point of output I and the point of connection .4 of resistor 22 with the anode circuit. Likewise output 2 is taken directly from the cathode I8. The schematic diagram Vof Fig. 5 illustrates the bridge arrangement of this circuit and the function of the variable resistor 2l. Variation of this resistor varies the relative magnitudes of the output voltages, that of output I increasing linearly with the value of resistor 2I, while that of output 2 is but slightly affected by such variation. Since resistor 20 equals resistor 2|, the feed-back voltages supplied tothe control electrode from the anode and cathode circuits are always equal, regardless of the setting of resistance 2'I. Consequently, the balance of the bridge circuit is undisturbed by Variations of resistance 27 to adjust the relative magnitudes of the output voltages.

By means of the circuits described in the foregoing, two output signals which are opposite in phase and of precisely the same time occurrence as the input signal, are obtained from a single input signal. The relative magnitudes of the output signals may be made equal or may be adjusted to meet the requirements of following circuits.

' By way of illustration only, and not in any sense by way of limitation, the following representative values are those which have been found suitable in a particular phase inverter circuit embodying my invention. In this receiver a type GVG triocle tube was employed as the phase inverter tube in accordance with the modification shown in Fig. 5 of the drawings. The values of the circuit constants were as follows:

Resistor 1522,000 ohms Resistor 20=1,000 ohms Resistor 21:1,000 ohms Resistor 22:.5 megohm Resistor 23:.5 megohm Resistor 19:500 ohms Resistor 27:1000 ohms potentiometer Capacitor 26=.1 microfarad Capacitor 28:.1 microfarad Thus it will be noted that the resistance in the cathode circuit of Fig. 5 between output 2 and ground is 1500 ohms, while the resistance between anode and ground may be varied from 1000 to 2000 ohms without disturbing the balance of the bridge.

While I have described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without actually departing from the invention. I therefore desire by f. the appended claims to cover al1 such changes and modifications as fall within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a system for isolating a single-ended source of signals which Vary with respect to a point of xed potential from the output of a single tube phase inverter comprising an electron discharge device having an anode, a cathode, and a control electrode, means for impressing signals from said source between said control electrode and said cathode, first and second output terminals connected to said anode and said cathode respectively, a series circuit connected between said terminals, said series circuit comprising a pair of resistances, means connecting said electrode to a point between said resistances in said series circuit, said last-named point being variable in potential with respect to said point of iixed potential, and resistance means connected between each of said output terminals and said point of fixed potential.

2. In combination with a source of signals, a phase inverter for producing opposed signals at two points comprising an electron discharge device having an anode connected to one of said points, a cathode connected to the other of said points, and a control electrode coupled to said source of signals, impedances connected between said control electrode and each of said points, and impedances connected between each of said points and said source of signals, said impedances being of such magnitude as to form a balanced bridge circuit of which said points form two opposite corners and said source of signals is connected across the remaining corners, whereby said source is isolated from said two points to prevent feedback of distortion thereto.

3. In combination in an amplifier, a source of signals which vary with respect to a point of xed potential, an electron discharge device having an anode, a cathode, and a control electrode, output means connected between said anode and said point of fixed potential, output means connected between said cathode and saidpoint of fixed potential, means for impressing signals from said source on said electrode, and means for isolating said source of signals from said output means, said means comprising equal resistances connected between said control electrode and each of said output means, and equal resistances connected between each of said output means and said point of fixed potential.

4. In combination. a first electron discharge device having input means and output means for providing a signal which varies with respect to a point of xed potential, a second electron discharge device having an anode, a cathode, and a control electrode; means for connecting said control electrode with said output means of said first electron discharge device, an output terminal connected to said anode, an output terminal connected to said cathode, and meansfor isolating said rst electron discharge device from said terminals to prevent feedback of distortions thereto, said means comprising a pair of equal resistances y connected between said terminals and said control electrode, and a second pair of equal resistances connected between said terminals and said point of fixed potential.

5. In combination with an electron discharge device having an anode, a cathode, and a control electrode, a bridge circuit comprising a pair of equal impedances connected between a point of fixed potential and said anode and said cath- 1 and said cathode, first and second output terminals connected to said anode and said cathode respectively, a variable resistance connected to said anode, a fixed resistor connectedvto said cathode, and means for isolating said single-ended source of signals from said output terminals,

said'means comprising equal resistances connected between saidr contres encarece, and. said vari` able resistance and said fixed resistor respectively, and equal resistances connected between said point of fixed potential and said variable resistance and said iixed resistor respectively.

'7. In combination, a first electron discharge device having input means and output means for providing a signal which varies with respect to a point of xed potential, a second electron discharge device having an anode, a cathode, and a control electrode, means for connecting said `control electrode with said output means, output terminals connected respectively to said anode and said cathode, a fixed resistor connected to said cathode, a variable resistor connected to said anode, and means for isolating said iirst electron discharge device from said terminals to prevent feedback of distortions thereto, said means comprising a pair of equal resistances connected respectively between said control electrode and said fixed and variable resistors, and a pair of equal resistances connected respectively between ksaid point of fixed potential and said fixed and variable resistors.

8. In combination with an electron discharge device having an anode, a cathode, and a control electrode, a bridge circuit comprising a pair of impedances connected between a point of i-lxed potential and said anode and said cathode respectively, and a second pair of impedances connected rbetween said control electrode and said anode and said cathode respectively, and a source of signals connected between said control electrode and said point of iixed potential, said second pair of impedances being proportioned with respect to each other and to the impedances of said first pair of impedances to prevent variations of the potential of said anode from being supplied to said electrode.

9. In an amplifier having a single ended source of signals which vary with respect to a point of fixed potential, the combination of, an electron discharge device having an anode, a cathode, and a control electrode, means for impressing signals from said source between said control electrode and said cathode, a first outputcircuit connected between said anode and said point, a second output circuit connected between said cathode and said point, one, of said output circuits comprising a pair of serially connected resistances and the other of said output circuits comprising a fixed resistance and a variable resistance in series therewith, and means for isolating said single ended source of signals from said output circuits, said means comprising equal resistances con.. nected respectively between said electrode and the common point of` said pair of serially connected resistances and between said electrode and the common point of said iixed and variable resistances.

10. In combination, a source of signals, an electron discharge device having a control electrode coupled tosaid source, an anode, and ra cathode, a first resistance connected between said anode and a point of fixed potential, a second re-f sistance connected between said cathode and said pointand means fory isolating said source from `said output circuit comprising a third resistance connected between said electrode and said anode,

.a fourth resistance connected between said electrode and said cathode, the ratio of said rst resistance to said third resistance being equal to the ratio of said second resistance to said fourth resistance.

SEYMOUR BERKOFF. 

